#31
|
|||
|
|||
Rockets
"Matthew F Funke" wrote in message ... No disagreement here. I just wanted to avoid the notion that a rocket needs to "push against" the ground, air, previously expelled propellant, or any other thing that is sitting out the back end when the rocket fires in order to work. (Rockets work better in vacuum than in air, in fact.) Right. I think ultimately we're in agreement here. -- -- With Best Regards, Matthew Funke ) |
#32
|
|||
|
|||
Rockets
Ian Woollard wrote:
Joann Evans wrote in message ... Ian Woollard wrote: Joann Evans wrote in message ... rockets ... are the only way known in current physics to make something move in a vacuum. That's not actually true; electromagnetic tethers and solar sails also work among several other options. Okay, but Newton's Third Law is still involved, momentum is still transferred. Big deal, Newton's third law and momentum transfer happen when I play basketball. That doesn't make me a rocket either. Are you playing it in free fall? Throw that basketball, and see what happens to you. Basketballs are acceptable reaction mass. Rockets have one or more rocket engines. Neither an electromagnetic tether nor a solar sail have rocket engines. Repeating: okay. I agree with that. Strictly speaking, this is not a rocket. |
#33
|
|||
|
|||
Rockets
"Joann Evans" wrote:
And indeed, as an atmosphere *impedes* the exhaust gases, rockets work *better* in vacuum, and are the only way known in current physics to make something move in a vacuum. [snip] This depends much more on the definition of vacuum than on anything else. If your definition is the ordinary definition then this is not true, as solar sails, mag sails, and electrodynamic tethers can change momentum in the "vacuum" of space. If your definition is a gasless, "perfect vacuum", then there are still solar sails and electrodynamic tethers. Only when you consider absolute, perfect vacuums without light, or any force gradients would your statement be true. |
#34
|
|||
|
|||
Rockets
In article ,
John Schoenfeld wrote: ... ... ellastic. ... ... ... ellastic ... ... I have often wondered why idiosyncratic misspelling so often coincides with crackpotism. Anyone know? (It is certainly a helpful shibboleth.) |
#35
|
|||
|
|||
Rockets
"Bruce Janson" wrote in message ... In article , John Schoenfeld wrote: .. ... ellastic. ... .. ... ellastic ... .. I have often wondered why idiosyncratic misspelling so often coincides with crackpotism. Anyone know? (It is certainly a helpful shibboleth.) Speaking for myself, the poor spelling and crackpotism are both caused by a self inflicted education. I've been thinking about suing myself for the defficiencies in learning. John Hare |
#36
|
|||
|
|||
Rockets
|
#37
|
|||
|
|||
Rockets
Joe Strout wrote:
[snip] All that needs to be done is to make the upwards push a greater impulse than the downwards push - the rocket would essential jerk its way upwards - after all there is no "conservation of displacement" with such an inertial system. There is conservation of momentum, and you just proposed to violate it. This is a stiction (static friction) drive, and works only when in contact with some other body. The movement comes from the difference between static and sliding friction. And, BTW, if you want a drive that only works when in contact wiith a larger body, there are much better ones (the wheel comes to mind). Such a drive is utterly useless in space, however. Jerk your rocket around all you want, it'll never make any net progress at all. Cheers, - Joe One more reason for cheap access at least to LEO: Everyone who thinks they've got a reactionless drive can take a prototype up there, put it outside the ship, and then they can put up, or shut up. (I know, there are cheaper ways of doing this [suspend it, and see if you get a unidirectional deflection, instead of gyrating or oscillating around the perpindicular], but my approach is instinctively unambiguous. This, after all, is where the thing is supposed to work.) It would be even more interesting, if the losers have to find their own way back to the ground..... |
#38
|
|||
|
|||
Rockets
John Schoenfeld wrote:
[snip] Um, yes, it is. No it is not. Imagine a stationary black-box floating in space. One wall of the box is hard iron and the opposite side is ellastic. If a ball is thrown from the middle at the hard iron wall there will be a high-impulse transfer of momentum from the ball to the box. Relative from the center of the box (which at this point is moving), the ball now approaches the opposite ellastic wall in which it inevitably collides with and transfers the same momentum but in the opposite direction bringing the box to rest again. However, the elastic wall collision was low-impulse and took longer for the momentum to be conservered. Irrespective of momentum conservation, there is an overall displacement. At this point we have the box at rest yet it is displaced from its original position, however in future time this same effect will occur but in the opposite direction and thus the overal motion of this contraption would be to OSCILLATE about the original position. So technically speaking, its not inertial propulsion yet as the center of mass is constant. So the third and final requirement would to have a constant stream of balls colliding just as the first one thus always staying one step ahead of the "backwards oscillation phase". I think some past claims of reactionless drives that allegedly reduced their weight (though never to zero, it seems) on scales, had more to do with a similar phenomenon in the springs of the scale, then actually providing a net upward force. Time your oscillations right, and you can fool the scale, but not Mother Nature.... |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
Alternative to Rockets | George Kinley | Science | 53 | March 31st 04 02:45 AM |
Von Braun rockets on Encyclopedia Astronautica | Pat Flannery | Space Science Misc | 41 | November 11th 03 08:10 AM |
The Life and Death of Russia's Space Shuttle Program , from Pravda | Locz | Space Shuttle | 0 | September 4th 03 02:49 PM |
Rockets | George Kinley | Science | 29 | August 1st 03 06:06 AM |
"Why I won't invest in rockets for space tourism ... yet" | RAILROAD SPIKE | Space Station | 0 | July 30th 03 12:06 AM |